Each country has different regulations, but what is clear is that if children are still in school, let alone wearing school uniforms to this gambling place, it is an unethical action. Gambling houses should place restrictions on visitors entering and gambling. It is true that there is no age limit for gambling, but wearing school uniforms should be prohibited, especially if someone cannot earn their own money, money used for gambling from their parents is certainly detrimental to the younger generation.
In my country, although gambling must be done secretly, if small children come, they are not allowed to come inside, especially those who are still wearing school uniforms. Gambling uses money, if children are allowed to gamble even though they are not working, it will have a bad impact on children, causing them to steal, skip school, and so on which will make their future bleak. Because even adults who cannot control themselves when gambling can have their finances ruined, let alone children who are still at school.
Maybe it's a good thing that gambling places have visitor limits or can see what kind of people can join in gambling, indeed with them being school children who are still in uniform and going in and gambling is very unethical, but if the children are already familiar with gambling in the sense that they are always want to gamble, maybe they will do anything, such as wearing clothes other than school uniforms, because even if they like gambling, I think they already understand that if they are in uniform and gambling is not allowed. Moreover, as you said, of course those who are still in uniform most likely cannot make their own money, of course they use the money from their parents to gamble. what is feared is that they will become addicted and become more daring to do things that carry big risks such as stealing.
Even those who already have jobs and are able to make money often experience many bad effects, but even that is due to the mistakes of each individual who gambles too much. with those who are still in school uniform and cannot make money, it is highly discouraged to gamble, even if I had a gambling casino, I would not allow them to gamble if they were still at school.